Developing and Implementing Advanced Optical Diagnostics for the Investigation of Fuel and Flow Effects on Impinging Jet Flames

Experimental diagnostic techniques have been utilised and developed to investigate the flame wall interaction for impinging flames of propane, methane, hydrogen and syngas. Thermal imaging has been used to evaluate the plate temperatures and radiation losses at steady state. A methodology has been developed for temperature dependent emissivity materials. Schlieren and direct imaging have been used to visualise flame shapes and flow structure. A methodology has been developed to quantify the relative effects of visual turbulent structures on the flame wall interaction. High speed schlieren has been used to assess the time dependent flame front propagation following ignition at various ignition locations.

The combination of these techniques has allowed the flame wall interaction to be analysed for fuel composition, thermal loading, equivalence ratio, nozzle-to-plate distance, Reynolds number, geometry and fuel exit velocity. It has been found that fuel composition significantly affects the wall temperature profiles even at similar nozzle conditions. Mixing in different regions of the impingement configuration caused significant differences in the wall temperature profiles for the different fuels due to differences in diffusivity and laminar flame speed. Syngas premixed flames produce similar wall temperature profiles near the lift-off limit but at different equivalence ratios and Reynolds numbers, due to the similar turbulence shown in the schlieren images. Plate material and nozzle-to-plate distance significantly affected the wall temperature profiles. Radiation losses from the plate helped to explain the differences in heat transfer for the different conditions.

Delays in the initial downwards propagation were observed for the hydrogen flames. The competing factors of the upstream propagation and heat production, causing decelerations and accelerations of the flame front respectively, differed significantly for different fuels and conditions. The propagation of the flame front immediately after ignition was observed to be very complex, changing significantly for relatively small changes in nozzle conditions.